1. Field of the Invention
The present invention relates to transmission of code data of images.
2. Description of Prior Art
Communication of image data uses a public line network previously, but as the Internet becomes popular, image data are also sent through the Internet. By using the Internet, communication cost is decreased and communication time becomes shorter.
There are various communication protocols for the Internet, such as HyperText Transfer Protocol (HTTP) for browsing a home page, File Transfer Protocol (FTP) for file transfer and Simple Mail Transfer Protocol (SMTP) for electronic mail (hereinafter referred to as e-mail).
In order to prevent web hacking to an internal system of users, a firewall is provided generally at a connection between the Internet and a network such as a local area network. The firewall has a function to control communication protocols which pass between the Internet and a user in the network, and it limits protocols which pass the firewall. Usually, protocols for e-mail are allowed to pass the firewall. Therefore, when an image data is sent through the Internet, an e-mail delivery system is used.
However, when an e-mail with attachment of image data is sent through the Internet, it is a problem that the mail size is limited. As the number of the functions equipped for a recent image forming apparatus such as a printer or a multi-functional peripheral is increased and the quality thereof become higher, the size of images obtained by the image forming apparatus is increased to about ten megabytes, and it would be increased further in the future. On the other hand, a mail server which collects and delivers e-mails generally limits the size of e-mail that can be transmitted. The size limit is for example one megabyte. Therefore, when the size of an image file exceeds the size limit, an e-mail attached with the image file would be refused to be received.
When the size of image data is large, if the image data is divided into a plurality of data having a size smaller than the limit, it can be sent through the mail server to a user. Then, a large file is divided into a plurality of small files, and each of the small files is attached to an e-mail. At the user's terminal, the attachment of the divided files is received, and the original file is recovered from the files. However, in this e-mail transmission of divided files, only a part of the entire image data is included in each divided file attached to an e-mail. Therefore, the contents of the entire image cannot be gotten by a user until all the e-mails are received.
In a facsimile apparatus disclosed in Japanese Patent laid open Publication 6-152979/1997, progressive code data of image data are obtained by reducing the image data successively and by encoding them hierarchically, and the code data are sent with facsimile transmission. The image data are encoded for each resolution, and the encoded data for each resolution are transmitted. At the second transmission and thereafter, difference data from the data of the resolution already received is transmitted. In this method, it is not necessary to divide the image data because a public line network has no limitation on file size. However, the transmission takes a long time. Further, when an image consisting of a plurality of pages are received, the data is received page by page. Therefore, a user cannot understand a general outline of the entire contents at an early stage.